Fixed #17615 -- Corrected unique field validation when using multitable...

Fixed #17615 -- Corrected unique field validation when using multitable inheritance. The validation used wrong pk value if the parent and child model had different pk fields. Thanks ungenio for the report and patch.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@17920 bcc190cf-cafb-0310-a4f2-bffc1f526a37